The present invention relates to a motor-driven compressor that has in the housing thereof an electric motor and a compression mechanism compressing refrigerant gas by the rotation of the electric motor.
Generally, a motor-driven compressor accommodates in a metal housing thereof an electric motor and a compression mechanism compressing refrigerant gas by the rotation of the electric motor. This kind of motor-driven compressor is connected to an external refrigerant circuit and refrigerant gas flows in the housing and through the compression mechanism during the operation of the motor-driven compressor. When the motor-driven compressor is at a stop, refrigerant gas is cooled and liquefied and the liquefied refrigerant (hereinafter referred to as “liquid refrigerant”) tends to be accumulated in the housing of the motor-driven compressor. Liquid refrigerant contains lubricating oil. It is noted that a specific kind of lubricating oil mixed with liquid refrigerant reduces the electrical resistivity of liquid refrigerant. A conductive part such as a terminal of wiring may be located in the electric motor or in the vicinity thereof in the housing and is exposed to liquid refrigerant. When such conductive part is immersed in liquid refrigerant accumulated in the housing, the insulation between the conductive part and the housing may be deteriorated.
Japanese Patent Application Publication 2009-264279 discloses a motor-driven compressor that improves the insulation between a conductive part and a housing of the motor-driven compressor. The motor-driven compressor has an electric motor that has a stator including a coil. The coil is formed of three-phase conductive wires. The ends of the three-phase conductive wires are drawn out from the coil and bundled together to form a bundled part. A wiring connection part is formed at the end of the bundled part by connecting the ends of the conductive wires and the wiring connection part serves as a neutral point. The bundled part is inserted through an insulation tube and an extra length part is formed in the bundled part by elongating the shortest insulation distance between the wiring connection part and the housing. The insulating resistance between the wiring connection part and the housing is improved by extending the shortest insulation distance between the wiring connection part and the housing. Therefore, the deterioration of the insulation between the conductive part and the housing due to the immersion in liquid refrigerant may be prevented.
However, the motor-driven compressor disclosed in the Publication needs extra space in the housing for disposing the extra length part. The provision of the extra length part increases the size of the motor-driven compressor and, therefore, the degree of freedom of mounting the motor-driven compressor on a vehicle is deteriorated. Depending on the space limitation in mounting of the motor-driven compressor, the provision of the extra length part may make it extremely difficult to mount the compressor.
Liquid refrigerant accumulated in the housing during the stop of the motor-driven compressor is due to the refrigerant gas cooled and liquefied in the external refrigerant circuit, as well as the refrigerant gas cooled and liquefied in the housing.
The liquid refrigerant produced in the external refrigerant circuit and flowed into the housing adds to the accumulation of the liquid refrigerant in the housing.
In a case of a motor-driven compressor where the extra length part can not be provided due to space limitation, a conductive part tends to be immersed in liquid refrigerant, so that the insulation between the conductive part and a housing deteriorates.
Additionally, when liquid refrigerant is accumulated in the housing at a start-up of the motor-driven compressor, the liquid refrigerant is vaporized in the housing and the pressure in the housing is increased excessively.
In such a case, a larger torque is required at the start-up of the compressor, so that the load applied to the motor-driven compressor increases.
The present invention is directed to providing a motor-driven compressor that prevents liquid refrigerant from flowing into the housing of the compressor from the external refrigerant circuit to be accumulated in the motor-driven compressor so as to ensure the insulation of the conductive part of the motor-driven compressor.